Electrochemical Deposition of Elements in Aqueous Media

ABSTRACT

The disclosure relates to a method for the electrodeposition of at least one metal onto a surface of a conductive substrate. In some embodiments, the electrodeposition is conducted at a temperature from about 10° C. to about 70° C., about 0.5 atm to about 5 atm, in an atmosphere comprising oxygen. In some embodiments, the method comprises electrodepositing the at least one metal via electrochemical reduction of a metal complex dissolved in a substantially aqueous medium.

BACKGROUND

Electrodeposition of metals, including aluminum, at ambient temperatureshas been widely investigated owing to a variety of potentialapplications that include uses in corrosion-resistant applications,decorative coatings, performance coatings, surface aluminum alloys,electro-refining processes, and aluminum-ion batteries. Due to the largereduction potential of some metals, these materials have beenexclusively used in non-aqueous media. For example, baths that have beendeveloped for aluminum electrodeposition fall into three categories.These categories are inorganic molten salts, ionic liquids, andmolecular organic solvents. Inorganic molten salt baths require arelatively high temperature (e.g., >140° C.). And in some instances,such baths are prone to the volatilization of corrosive gases. Forexample, AlCl₃—NaCl—KCl baths suffer from the volatilization ofcorrosive AlCl₃ gas. In addition, baths that have been developed foraluminum electrodeposition have high energy consumption and materiallimitations of the substrate and apparatus.

Ionic liquid and organic solvent baths both allow electrodeposition of ametal, such as aluminum, at lower temperatures. For example, aluminumplating from room temperature ionic liquids has been the subject of anumber of studies over the past few years. Still, an industrial processfor aluminum electrodeposition from ionic liquids does not beenrealized, even though a manufacturing pilot plant was developed byNisshin Steel Co., Ltd. The plant was not considered economically viabledue to cost associated with materials and the need to perform plating inan inert atmosphere, free of humidity.

Commercial aluminum electroplating processes from organic solvents hasbeen deployed with limited success. As of now, only two processes,namely, the Siemens Galvano Aluminium (SIGAL) process andRoom-temperature Electroplated Aluminium (REAL) process have beendeployed. The SIGAL process is currently licensed to AlumiPlate, Inc.and yields high quality aluminum. However, organoaluminum processes areself-ignitable and extremely sensitive to atmospheric water.

SUMMARY

Disclosed herein is a method for the electrodeposition of at least onemetal onto a surface of a conductive substrate. The electrodeposition isperformed at a temperature from about 10° C. to about 70° C. and, insome instances, at a pressure of about 0.5 atm to about 5 atm, in anatmosphere comprising oxygen. The method of the various embodimentsdescribed herein comprises electrodepositing the at least one metal viaelectrochemical reduction of a metal complex dissolved in asubstantially aqueous medium.

DESCRIPTION OF THE FIGURES

The drawings illustrate generally, by way of example, but not by way oflimitation, various embodiments discussed in the present document.

FIG. 1 is a plot of a series for metal reductions versus that of protonreduction.

FIG. 2 is cyclic voltammograms for aluminum complexes at 1 Mconcentration in water (i) Al(Tf₂N)₃; and (ii) AlCl₃ on a 3 mm glassycarbon working electrode vs. a Ag/AgCl (3M NaCl) reference electrode andan aluminum counter electrode and a 50 mVs⁻¹ scan rate.

FIG. 3 is cyclic voltammograms for aluminum complexes in water (i) 6 Mp-TSA; (ii) 0.5 M Al(p-TSA)₆ (pH 0.24); (iii) 0.5 M Al(p-TSA)₄; (iv) 0.5M Al(p-TSA)₆ with pH adjusted to 1.35 with NH₄OH; and (v) 1 M AlCl₃ on a3 mm glassy carbon working electrode vs. a Ag/AgCl (3 M NaCl) referenceelectrode and an aluminum counter electrode and a 50 mVs⁻¹ scan rate.

FIG. 4 is cyclic voltammograms for aluminum complexes in water (i) 1 MAl(MS)₃ (pH 2.47); (ii) 3 M Al(MS)₁ (pH 3.15); and (iii) 1 M AlCl₃ on a3 mm glassy carbon working electrode vs. a Ag/AgCl (3 M NaCl) referenceelectrode and an aluminum counter electrode and a 50 mVs⁻¹ scan rate.

FIG. 5 is a scanning electron microscopy (SEM)/energy-dispersive X-ray(EDX) spectroscopy image of 20 AWG copper wire plated to a thickness inexcess of 10 μm with aluminum.

DESCRIPTION Introduction

Many commercially important elements from the periodic table cannot beeasily electrodeposited from aqueous solutions because their reductionpotentials can be much larger than the electrochemical window for water(e.g., the over-potential for the evolution of hydrogen gas due to watersplitting). The various embodiments described herein provide an approachwhereby the reduction potential of metals is “tuned” in a way that theyare amendable to electrodeposition from aqueous solutions. In oneembodiment, the reduction potential of the metal is tuned by selectingligands that change the reduction potential of the metals such that themetal can be electrodeposited from an aqueous solution without, e.g.,hydrogen gas generation. In other embodiments, the ligands are chosen insuch a way that they affect the reduction potential of the metal center,thermodynamically, such that the reduction of the metal center occursprior to the hydrogen evolution overpotential.

Some embodiments described herein, therefore, are directed to a methodfor the electrodeposition of at least one metal onto a surface of aconductive substrate. In some embodiments, the electrodeposition isconducted at a temperature from about 10° C. to about 70° C. (e.g.,about 10° C. to about 25° C.; about 10° C. to about 40° C.; about 15° C.to about 50° C.; about 25° C. to about 50° C.; or about 30° C. to about50° C.), about 0.5 atm to about 5 atm (e.g., about 0.5 atm to about 2atm; 0.5 atm to about 1 atm; 1 atm to about 3 atm; 2 atm to about 5 atmor about 2 atm to about 3 atm), in an atmosphere comprising oxygen(e.g., in an atmosphere comprising about 1 to about 100% oxygen; about 5to about 50% oxygen; about 10 to about 30% oxygen; about 15 to about 30%oxygen; about 20 to about 80% oxygen or about 25 to about 75% oxygen,the balance of the atmosphere comprising gases including nitrogen,carbon dioxide, carbon monoxide, water vapor, etc.). In someembodiments, the method comprises electrodepositing the at least onemetal via electrochemical reduction of a metal complex dissolved in asubstantially aqueous medium. It should be understood that the method ofthe various embodiments described herein can also be conducted underconditions wherein the medium also contains at least some amount ofdissolved oxygen (e.g., dissolved oxygen in the water present in themedium).

Metals

The metals that can be electrodeposited using the electrodepositionmethods described herein are not limited. Electron withdrawing approachis applicable to at least the metals in Groups 2, 4, 5, 7, and 13.Metals useful in the methods described herein include metals having ingeneral a Pauling electronegativity below 1.9 (e.g., about 1.3 to about1.6; about 1.7 to about 1.9; and about 1.6 to about 1.9). Generallyspeaking, such metals would be considered nearly impossible to plate inwater at high efficiency; or such metals would encounter problems withhydrogen embrittlement.

The electromotive series for the process M^(n+)+ne⁻→M, illustrated inFIG. 1 shows an example of a series for metal reductions versus that ofproton reduction. Metals with a negative reduction are considered moredifficult to reduce than protons in the presence of an acid source andare able to do so based on the high overpotential for proton reduction.These metals may have a reduced cathodic plating efficiency as a resultof competitive hydronium ion reduction or an increased risk of hydrogenembrittlement. According to the various embodiments described herein, byaddition of a suitable electron withdrawing ligand, any metal on thiselectromotive series may benefit from the reduction potential being mademore positive by the inductive effect of the ligand thus creating asituation of increased efficiency for the plating process as comparedwith the hydrogen reduction overpotential. Examples of metals that arein the “electromotive series” include gold, platinum, iridium,palladium, silver, mercury, osmium, ruthenium, copper, bismuth,antimony, tungsten, lead, tin, molybdenum, nickel, cobalt, indium,cadmium, iron, chromium, zinc, niobium, manganese, vanadium, aluminum,beryllium, titanium, magnesium, calcium, strontium, barium, andpotassium. See, e.g., EP0175901, which is incorporated by reference asif fully set forth herein.

In some embodiments, suitable metals for use in the various methodsdescribed herein include metals that have a reduction potential fromabout 0 V to about −2.4 V.

In some embodiments, the metals that can be electrodeposited using theelectrodeposition methods described herein can be “reactive” or“non-reactive” metals. The term “reactive,” as used herein, generallyrefers to metals that are reactive to, among other things, oxygen andwater. Reactive metals include self-passivating metals. Self-passivatingmetals contain elements which can react with oxygen to form surfaceoxides (e.g., such as the oxides of, but not limited to, Cr, Al, Ti,etc.). These surface oxide layers are relatively inert and preventfurther corrosion of the underlying metal.

Examples of reactive metals include aluminum, titanium, manganese,gallium, vanadium, zinc, zirconium, and niobium. Examples ofnon-reactive metals include tin, gold, copper, silver, rhodium, andplatinum.

Additional metals that can be electrodeposited using theelectrodeposition methods described herein include molybdenum, tungsten,iridium, gallium, indium, strontium, scandium, yttrium, magnesium,manganese, chromium, lead, tin, nickel, cobalt, iron, zinc, niobium,vanadium, titanium, beryllium, and calcium.

Metal Complex

The metal complexes of the various embodiments described herein comprisea metal center and ligands associated with the metal center. In someembodiments, at least one of the ligands associated with the metalcenter is an electron withdrawing ligand.

Metal complexes of the various embodiments described herein includemetal complexes of the formula:

(M₁L_(a)L_(b))_(p)(M₂L_(a)L_(b))_(d)

wherein M₁ and M₂ each, independently represents a metal center; L is anelectron withdrawing ligand; p is from 0 to 5; and d is from 0 to 5; ais from 1 to 8 (e.g., from 1 to 4; from 0.5 to 1.5; from 2 to 8; 2 to 6;and 4 to 6); and b is from 1 to 8 (e.g., from 1 to 4; from 0.5 to 1.5;from 2 to 8; 2 to 6; and 4 to 6). The metal complexes contemplatedherein, therefore, can include metal complexes comprising more than onemetal species and can even include up to ten different metal specieswhen p and d are each 5. In addition, each of the metal complexes canhave the same or different ligands around the metal center. Thus, forexample, one can have two different metal complexes (e.g., when p is 1and d is 1), the first being Cr(SO₃R¹)_(a); and the second beingMo(SO₃R¹)_(a). This combination of metal complexes can be used toelectrodeposit a CrMo alloy on a surface of a substrate.

As used herein, the term “metal center” generally refers to a metalcation of a metal from Groups 2, 4, 5, 7, and 13. But it should beunderstood that metal cations from Groups 2, 4, 5, 7, and 13 can bealloy plated using the methods described herein with metal cations fromGroups 3, 6, 8, 9, 10, 11, and 12.

Some examples of “metal centers” include a cation of aluminum (e.g.,Al⁺³), titanium (e.g., Ti²⁺, Ti³⁺, and Ti⁺⁴), manganese (e.g., Mn²⁺ andMn³⁺), gallium (e.g., Ga⁺³), vanadium (e.g., V⁺², V³⁺, and V⁺⁴), zinc(e.g., Zn²⁺), zirconium (e.g., Zr⁴⁺), niobium (e.g., Nb⁺³ and Nb⁺⁵), tin(e.g., Sn⁺² and Sn⁺⁴), gold (e.g., Au⁺¹ and Au⁺³), copper (e.g., Cu⁺¹and Cu⁺³), silver (e.g., Ag⁺¹), rhodium (e.g., Rh⁺² and Rh⁺⁴), platinum(e.g., Pt⁺² and Pt⁺⁴), chromium (e.g., Cr⁺², Cr⁺³, and Cr⁺⁶), tungsten(e.g., W⁺⁴ and W⁺⁵), and iridium (e.g., Ir⁺¹ and Ir⁺⁴).

As defined herein, the term “electron withdrawing ligand” generallyrefers to a ligand or combination of one or more ligands (e.g., two tothree; two to six; three to six; or four to six ligands) associated withthe metal center, wherein the ligand or ligands are sufficientlyelectron withdrawing such that the reduction potential of the metalcenter in the metal complex is decreased below the over-potential forthe evolution of hydrogen gas due to water splitting. The term“over-potential for the evolution of hydrogen gas due to watersplitting” refers, in some instances, to a potential more negative than−1.4 V versus Ag/AgCl, where one generally observes significant hydrogengeneration.

In some embodiments, electron withdrawing ligands can be ligands whereinthe conjugate acid of the ligand has a pKa of from about 2 to about −5(e.g., about −1.5 to about −4; about −2 to about −3; about −2 to about−4; about −1 to about −3; and about 2 to about −2).

In some embodiments, the ligands that are useful in the methodsdescribed herein include sulfonate ligands, sulfonimide ligands,carboxylate ligands; and β-diketonate ligands.

Examples of sulfonate ligands include sulfonate ligands of the formula⁻OSO₂R¹, wherein R¹ is halo; substituted or unsubstituted C₆-C₁₈-aryl;substituted or unsubstituted C₁-C₆-alkyl; substituted or unsubstitutedC₆-C₁₈-aryl-C₁-C₆-alkyl.

Examples of sulfonimide ligands include ligands of the formula⁻N(SO₃R¹), wherein R¹ is wherein R¹ is halo; substituted orunsubstituted C₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl;substituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl.

Examples of carboxylate ligands include ligands of the formula R¹C(O)O⁻,wherein R¹ is wherein R¹ is halo; substituted or unsubstitutedC₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl; substituted orunsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl. Other examples of carboxylateligands include ligands of the formula ⁻O(O)C—R²—C(O)O⁻ wherein R² is(C₁-C₆)-alkylenyl or (C₃-C₆)-cycloalkylenyl.

In some embodiments, the ligands can be ligands such as the onesdescribed in Scheme I, herein.

Specific examples of sulfonate ligands include sulfonate ligands of theformulae:

Specific examples of sulfonimide ligands include sulfonimide ligand ofthe formula:

wherein each R¹ is independently F or CF₃. In some embodiments, each R¹is the same and can be F or CF₃.

Examples of β-diketonate ligands includes ligands of the formula:

where R³, R⁴, and R⁵ may be substituted or unsubstituted C₆-C₁₈-aryl;substituted or unsubstituted C₁-C₆-alkyl; or substituted orunsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl, with the understanding that allresonance structures of the two β-diketonate ligands picture above, arealso included.

In some embodiments, α-diketonate ligands can have the formulaR⁶C(═O)CHCHC(═O)R⁷, wherein R⁶ and R⁷ may be selected from alkoxy groups(e.g., methoxy, ethoxy, propoxy, hexyloxy, octyloxy, and the like),aryloxy groups (e.g., phenoxy, biphenyloxy, anthracenyloxy, naphthyloxy,pyrenyloxy, and the like), and arylalkyloxy groups (e.g., benzyloxy,naphthyloxy, and the like).

In one embodiment, the ligand is acetylacetonate, also known as an“acac” ligand.

Some of the ligands described herein are shown in their deprotonatedform (e.g., in the form of their conjugate base). Contemplated hereinare also the ligands in their conjugate acid form such as, for example:

In addition, contemplated herein are ligands that can be in equilibriumbetween their conjugate acid and conjugate base forms, such as, forexample:

Various ratios of metal to ligand are contemplated for use in themethods described herein. For example, the ratio of metal to ligand canbe from about 1:50 to about 1:1 (e.g., from about 1:50 to about 1:25;about 1:30 to about 1:15; about 1:15 to about 1:5; about 1:10 to about1:1; and about 1:10 to about 1:5).

The terms “halo,” “halogen,” or “halide” group, as used herein, bythemselves or as part of another substituent, mean, unless otherwisestated, a fluorine, chlorine, bromine, or iodine atom.

The term “aryl,” as used herein, refers to substituted or unsubstitutedcyclic aromatic hydrocarbons that do not contain heteroatoms in thering. Thus aryl groups include, but are not limited to, phenyl,azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl,triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenylenyl,anthracenyl, and naphthyl groups. In some embodiments, aryl groupscontain about 6 to about 18 carbons (C₆-C₁₈; e.g., C₆-C₁₂; C₆-C₁₀; andC₁₂-C₁₈) in the ring portions of the groups. Representative substitutedaryl groups can be mono-substituted or substituted more than once, suchas, but not limited to, 2-, 3-, 4-, 5-, or 6-substituted phenyl or 2-8substituted naphthyl groups.

The term “alkyl,” as used herein, refers to substituted or unsubstitutedstraight chain and branched alkyl groups and cycloalkyl groups havingfrom 1 to 50 carbon atoms (C₁-C₅₀; e.g., C₁₀-C₃₀, C₁₂-C₁₈; C₁-C₂₀,C₁-C₁₀; C₁-C₈; C₁-C₆, and C₁-C₃). Examples of straight chain alkylgroups include those with from 1 to 8 carbon atoms (C₁-C₈) such asmethyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octylgroups. Examples of branched alkyl groups include, but are not limitedto, isopropyl, iso-butyl, sec-butyl, t-butyl, neopentyl, isopentyl,2,2-dimethylpropyl, and isostearyl groups. Examples of cycloalkyl groupsinclude cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups.

The term “substituted” as used herein refers to a group (e.g., alkyl andaryl) or molecule in which one or more hydrogen atoms contained thereonare replaced by one or more “substituents.” The term “substituent” asused herein refers to a group that can be or is substituted onto amolecule or onto a group. Examples of substituents include, but are notlimited to, a halogen (e.g., F, Cl, Br, and I); an oxygen atom in groupssuch as hydroxyl groups, alkoxy groups, aryloxy groups, aralkyloxygroups, oxo(carbonyl) groups, carboxyl groups including carboxylicacids, carboxylates, and carboxylate esters; a sulfur atom in groupssuch as thiol groups, alkyl and aryl sulfide groups, sulfoxide groups,sulfone groups, sulfonyl groups, and sulfonamide groups; a nitrogen atomin groups such as amines, hydroxylamines, nitriles, nitro groups,N-oxides, hydrazides, azides, and enamines; and other heteroatoms invarious other groups. Non-limiting examples of substituents that can bebonded to a substituted carbon (or other) atom include F, Cl, Br, I, OR,OC(O)N(R)₂, CN, NO, NO₂, ONO₂, azido, CF₃, OCF₃, R, O (oxo), S (thiono),C(O), S(O), methylenedioxy, ethylenedioxy, N(R)₂, SR, SOR, SO₂R,SO₂N(R)₂, SO₃R, C(O)R, C(O)C(O)R, C(O)CH₂C(O)R, C(S)R, C(O)OR, OC(O)R,C(O)N(R)₂, OC(O)N(R)₂, C(S)N(R)₂, (CH₂)₀₋₂N(R)C(O)R, (CH₂)₀₋₂N(R)N(R)₂,N(R)N(R)C(O)R, N(R)N(R)C(O)OR, N(R)N(R)CON(R)₂, N(R)SO₂R, N(R)SO₂N(R)₂,N(R)C(O)OR, N(R)C(O)R, N(R)C(S)R, N(R)C(O)N(R)₂, N(R)C(S)N(R)₂,N(COR)COR, N(OR)R, C(═NH)N(R)₂, C(O)N(OR)R, or C(═NOR)R, wherein R canbe, for example, hydrogen, alkyl, acyl, cycloalkyl, aryl, aralkyl,heterocyclyl, heteroaryl, or heteroarylalkyl.

The term “acyl” as used herein refers to a group containing a carbonylmoiety wherein the group is bonded via the carbonyl carbon atom. Thecarbonyl carbon atom is also bonded to another carbon atom, which can bepart of a substituted or unsubstituted alkyl, aryl, aralkyl cycloalkyl,cycloalkylalkyl, heterocyclyl, heterocyclylalkyl, heteroaryl,heteroarylalkyl group or the like. In the special case wherein thecarbonyl carbon atom is bonded to a hydrogen, the group is a “formyl”group, an acyl group as the term is defined herein. An acyl group caninclude 0 to about 12-40, 6-10, 1-5 or 2-5 additional carbon atomsbonded to the carbonyl group. An acryloyl group is an example of an acylgroup. An acyl group can also include heteroatoms within the meaninghere. A nicotinoyl group (pyridyl-3-carbonyl) is an example of an acylgroup within the meaning herein. Other examples include acetyl, benzoyl,phenylacetyl, pyridylacetyl, cinnamoyl, and acryloyl groups and thelike. When the group containing the carbon atom that is bonded to thecarbonyl carbon atom contains a halogen, the group is termed a“haloacyl” group. An example is a trifluoroacetyl group.

The term “aralkyl,” “arylalkyl,” and “aryl-alkyl” as used herein refersto alkyl groups as defined herein in which a hydrogen or carbon bond ofan alkyl group is replaced with a bond to an aryl group as definedherein. Representative aralkyl groups include benzyl and phenylethylgroups.

The term “heteroaralkyl” and “heteroarylalkyl” as used herein refers toalkyl groups as defined herein in which a hydrogen or carbon bond of analkyl group is replaced with a bond to a heteroaryl group as definedherein.

The term “heterocyclyl” as used herein refers to substituted orunsubstituted aromatic and non-aromatic ring compounds containing 3 ormore ring members, of which, one or more is a heteroatom such as, butnot limited to, N, O, and S. Thus, a heterocyclyl can be acycloheteroalkyl, or a heteroaryl, or if polycyclic, any combinationthereof. In some embodiments, heterocyclyl groups include 3 to about 20ring members, whereas other such groups have 3 to about 15 ring members.In some embodiments, heterocyclyl groups include heterocyclyl groupsthat include 3 to 8 carbon atoms (C₃-C₈), 3 to 6 carbon atoms (C₃-C₆) or6 to 8 carbon atoms (C₆-C₈). A heterocyclyl group designated as aC₂-heterocyclyl can be a 5-ring with two carbon atoms and threeheteroatoms, a 6-ring with two carbon atoms and four heteroatoms and soforth. Likewise a C₄-heterocyclyl can be a 5-ring with one heteroatom, a6-ring with two heteroatoms, and so forth. The number of carbon atomsplus the number of heteroatoms equals the total number of ring atoms. Aheterocyclyl ring can also include one or more double bonds. Aheteroaryl ring is an embodiment of a heterocyclyl group. The phrase“heterocyclyl group” includes fused ring species including those thatinclude fused aromatic and non-aromatic groups. Representativeheterocyclyl groups include, but are not limited to piperidynyl,piperazinyl, morpholinyl, furanyl, pyrrolidinyl, pyridinyl, pyrazinyl,pyrimidinyl, triazinyl, thiophenyl, tetrahydrofuranyl, pyrrolyl,oxazolyl, imidazolyl, triazolyl, tetrazolyl, benzoxazolinyl, andbenzimidazolinyl groups.

The term “alkoxy” as used herein refers to an oxygen atom connected toan alkyl group, including a cycloalkyl group, as are defined herein.Examples of linear alkoxy groups include but are not limited to methoxy,ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, and the like. Examples ofbranched alkoxy include but are not limited to isopropoxy, sec-butoxy,tert-butoxy, isopentyloxy, isohexyloxy, and the like. Examples of cyclicalkoxy include but are not limited to cyclopropyloxy, cyclobutyloxy,cyclopentyloxy, cyclohexyloxy, and the like. An alkoxy group can includeone to about 12-20 or about 12-40 carbon atoms bonded to the oxygenatom, and can further include double or triple bonds, and can alsoinclude heteroatoms. For example, an allyloxy group is an alkoxy groupwithin the meaning herein. A methoxyethoxy group is also an alkoxy groupwithin the meaning herein, as is a methylenedioxy group in a contextwhere two adjacent atoms of a structure are substituted therewith.

The term “aryloxy” and “heteroaryloxy” as used herein refers to anoxygen atom connected to an aryl group or a heteroaryl group, as theterms are defined herein. Examples of aryloxy groups include but are notlimited to phenoxy, naphthyloxy, and the like. Examples of heteroaryloxygroups include but are not limited to pyridoxy and the like.

The term “amine” as used herein refers to primary, secondary, andtertiary amines having, e.g., the formula N(group)₃ wherein each groupcan independently be H or non-H, such as alkyl, aryl, and the like.Amines include but are not limited to alkylamines, arylamines,arylalkylamines; dialkylamines, diarylamines, diaralkylamines,heterocyclylamines and the like; and ammonium ions.

The term “alkylenyl” as used herein refers to straight chain andbranched, saturated divalent groups having from 1 to 20 carbon atoms, 10to 20 carbon atoms, 12 to 18 carbon atoms, 1 to about 20 carbon atoms, 1to 10 carbons, 1 to 8 carbon atoms or 1 to 6 carbon atoms. Examples ofstraight chain alkylenyl groups include those with from 1 to 6 carbonatoms such as —CH₂—, —CH₂CH₂—, —CH₂CH₂CH₂—, —CH₂CH₂CH₂CH₂—, and—CH₂CH₂CH₂CH₂CH₂—. Examples of branched alkylenyl groups include—CH(CH₃)CH₂— and —CH₂CH(CH₃)CH₂—.

The term “cycloalkylenyl” as used herein refers to cyclic (mono- andpolycyclic, including fused and non-fused polycyclic), saturatedcarbon-only divalent groups having from 3 to 20 carbon atoms, 10 to 20carbon atoms, 12 to 18 carbon atoms, 3 to about 10 carbon atoms, 3 to 10carbons, 3 to 8 carbon atoms or 3 to 6 carbon atoms. Examples ofcycloalkylenyl groups include:

wherein the wavy lines represent the points of attachment to, e.g., themoieties —C(O)O⁻.

In some embodiments, the metal complex is at least one metal complex ofthe formula Al(SO₃R¹)_(n), wherein R¹ is halo; substituted orunsubstituted C₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl;substituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl; n is an integerfrom 2 to 8; and Al[N(SO₃R¹)₂]_(n), wherein R¹ is halo; substituted orunsubstituted C₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl;substituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl; and n is aninteger from 1 to 4.

Although not wishing to be bound by any specific theory, it is believedthat the metal complex can be additionally complexed with any speciespresent in the substantially aqueous medium that is capable ofcomplexing with the metal center. For example, in some instances, thesubstantially aqueous medium is buffered with a citrate buffer. It ispossible that the metal center of the metal complex can coordinate notonly with electron withdrawing ligands, but also with the citrate in thebuffer.

Substantially Aqueous Medium

The various embodiments of the methods described herein compriseelectrodepositing the at least one metal via electrochemical reductionof a metal complex dissolved in a substantially aqueous medium.

In some embodiments, the substantially aqueous medium comprises anelectrolyte. Generally speaking, the electrolyte can comprise anycationic species coupled with a corresponding anionic counterion (e.g.,some of the sulfonate ligands, sulfonimide ligands, carboxylate ligands;and β-diketonate ligands described herein). Cationic species include,for example, a sulfonium cation, an ammonium cation, a phosphoniumcation, a pyridinium cation, a bipyridinium cation, an amino pyridiniumcation, a pyridazinium cation, an oxazolium cation, a pyrazolium cation,an imidazolium cation, a pyrimidinium cation, a triazolium cation, athiazolium cation, an acridinium cation, a quinolinium cation, anisoquinolinium cation, an orange-acridinium cation, a benzotriazoliumcation, or a methimazolium cation. See, e.g., Published U.S. Appl. No.2013/0310569, which is incorporated by reference as if fully set forthherein.

An electrolyte can also comprise a cationic metal with a more negativereduction potential than the metal center in the metal complex of thevarious embodiments described herein. In other embodiments, theelectrolyte can comprise any suitable cation, including ⁺NR₄, whereineach R is independently hydrogen or C₁-C₆-alkyl; ⁺PR₄, wherein each R isindependently hydrogen or C₁-C₆-alkyl; imidazolium, pyridinium,pyrrolidinium, piperidinium; and ⁺SR₃; in combination with any suitableanion.

Examples of electrolytes include electrolytes comprising at least one ofa halide electrolyte (e.g., tetrabutylammonium chloride, bromide, andiodide); a perchlorate electrolyte (e.g., lithium perchlorate, sodiumperchlorate, and ammonium perchlorate); an amidosulfonate electrolyte;hexafluorosilicate electrolyte (e.g., hexafluorosilicic acid); atetrafluoroborate electrolyte (e.g., tetrabutylammoniumtetrafluoroborate); a sulfonate electrolyte (e.g., tinmethanesulfonate); and a carboxylate electrolyte.

Examples of carboxylate electrolytes include electrolytes comprising atleast one of compound of the formula R³CO₂ ⁻, wherein R³ is substitutedor unsubstituted C₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl.Carboxylate electrolytes also include polycarboxylates such as citrate(e.g., sodium citrate); and lactones, such as ascorbate (e.g., sodiumascorbate).

But in some embodiments, the metal complex can also act as anelectrolyte.

In sum, it should be understood that: (i) the metal complex can be theelectrolyte (e.g., have a dual function as metal complex forelectrodeposition and as electrolyte); (ii) when a buffer is used, themetal complex, in combination with the buffer, can be the electrolyte;(iii) the metal complex, in combination with a non-bufferingelectrolyte, can be the electrolyte; or (iv) the metal complex, incombination with a non-buffering electrolyte and an additionalnon-buffering salt (e.g., sodium chloride and potassium chloride), canbe the electrolyte.

In some embodiments the substantially aqueous medium has a pH of fromabout 1 to about 7 (e.g., about 2 to about 4; about 3 to about 6; about2 to about 5; about 3 to about 7; or about 4 to about 7). In otherembodiments, the substantially aqueous medium is buffered at a pH ofbetween about 1 and about 7 (e.g., about 2 to about 4; about 3 to about6; about 2 to about 5; about 3 to about 7; or about 4 to about 7) usingan appropriate buffer.

In some embodiments, the substantially aqueous medium comprises awater-miscible organic solvent. The water-miscible organic solventcomprises at least one of an C₁-C₆-alkanol (ethanol, methanol,1-propanol, and 2-propanol); a C₂-C₁₀-polyol (e.g., 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,3-propanediol, 1,5-propanediol,ethylene glycol, propylene glycol, diethylene glycol, and glycerol); a(poly)alkylene glycol ether (e.g, glyme and diglyme); aC₂-C₁₀-carboxylic acid (e.g., ethanoic acid, acetic acid, butyric acid,and propanoic acid); a C₂-C₁₀-ketone (e.g., acetone, 2-butanone,cyclohexanone, and acetylacetone); a C₂-C₁₀-aldehyde (e.g.,acetaldehyde); a pyrrolidone (e.g., N-Methyl-2-pyrrolidone); aC₂-C₁₀-nitrile (e.g., acetonitrile); a phthalate (e.g.,di-n-butylphthalate); a C₂-C₁₀-dialkylamine (e.g., diethylamine); aC₂-C₁₀-dialkylformamide (e.g., dimethylformamide); a C₂-C₁₀-dialkylsulfoxide (dimethyl sulfoxide); a C₄-C₁₀-heterocycloalkane (e.g.,dioxane and tetrahydrofuran); aminoalcohols (e.g., aminoethanol); and aC₄-C₁₀-heteroarylene (e.g., pyridine).

Substrate

Embodiments described herein are directed to a method for theelectrodeposition of at least one metal onto a surface of a conductivesubstrate.

As defined herein, the term “substrate” includes any material with aresistivity of less than 1 Ωm (at 20° C.). Some metallic substrates willnaturally have such a resistivity. But the requisite resistivity can beachieved for non-metallic substrates by methods known in the art. Forexample, through doping, as is the case for semi-conductors comprisingprimarily of silicon; or by pretreatment of the substrate with analternative coating technique to deposit a thin, adherent layer with asurface resistivity of less than 1 Ωm, as is the case for plastics,precoated with a metal such as copper.

Other substrates include, for example, plastics that are doped with acarbon material (e.g., carbon nanotubes and graphene) to the point wherethey are suitably conductive; and electron conductive polymers such aspolypyrrole and polythiophene.

Applications

In some embodiments, the methods described herein can be used toelectrodeposit at least one layer (e.g., at least two) of the at leastone (e.g., at least two) metal onto a surface of a substrate. In someembodiments, each layer can comprise one or more different metals. Inother embodiments, when there are at least two layers that areelectrodeposited, a first layer comprises different at least one metalrelative to the second layer.

The electrodeposition methods described herein can therefore be used toin a variety of different applications, including: electrodesposition ofcorrosing resistant alloys; generating biomedical coatings; generatingautomotive coatings; generating catalysis coatings; growing refractorymaterial over metallic substrates (e.g., materials used in kilns, powerplants, glass smelters, steel manufacturing, etc., which would have usefor growing refractory materials on an aluminum oxide layer to generatea ceramic coating with a metal backing); thermal barrier coatings for,e.g., gas turbines; water infrastructure coatings, to imbue theinfrastructure with, among other things, resistance to sulfates,alkaline conditions, and improved corrosion resistance towards hotwater; highway and aerospace infrastructure, to imbue the infrastructurewith improved corrosion against natural elements, salts, and de-icingfluids); nano-patterning and applications in electronics andlithography; generating metal alloys; improve adhesion of, e.g., paintto a surface by creating hydroxylic functionality on aluminum oxidelayers; electro-coat applications where, for example sharp edges on ametal surface are first coated with a second metal and the coated metalis subsequently cationic epoxy electrocoated); creating non-adhesivessubstrates by co-depositing nickel-Teflon on a substrate; generatingprimer coatings for e-coat applications, as well as aerospace andautomotive coatings; applications in galvanic corrosions, wheredissimilar metals may be in contact; metal purification; optics andradiator absorbers; light to thermal conversion devices; heatexchangers; creating coatings comprising nano- or microparticles ofdiamond, Teflon®, carbon black, talc, where the nano- or microparticlesare suspended in the substantially aqueous medium and they would beincluded in the plating.

The term “about” as used herein can allow for a degree of variability ina value or range, for example, within 10%, within 5%, or within 1% of astated value or of a stated limit of a range.

The term “substantially” as used herein refers to a majority of, ormostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%,98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range were explicitly recited. For example, arange of “about 0.1% to about 5%” or “about 0.1% to 5%” should beinterpreted to include not just about 0.1% to about 5%, but also theindividual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g.,0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range.The statement “about X to Y” has the same meaning as “about X to aboutY,” unless indicated otherwise. Likewise, the statement “about X, Y, orabout Z” has the same meaning as “about X, about Y, or about Z,” unlessindicated otherwise.

In this document, the terms “a,” “an,” or “the” are used to include oneor more than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive “or” unless otherwise indicated.In addition, it is to be understood that the phraseology or terminologyemployed herein, and not otherwise defined, is for the purpose ofdescription only and not of limitation. Any use of section headings isintended to aid reading of the document and is not to be interpreted aslimiting. Further, information that is relevant to a section heading mayoccur within or outside of that particular section. Furthermore, allpublications, patents, and patent documents referred to in this documentare incorporated by reference herein in their entirety, as thoughindividually incorporated by reference. In the event of inconsistentusages between this document and those documents so incorporated byreference, the usage in the incorporated reference should be consideredsupplementary to that of this document; for irreconcilableinconsistencies, the usage in this document controls.

In the methods described herein, the steps can be carried out in anyorder without departing from the principles of the invention, exceptwhen a temporal or operational sequence is explicitly recited.Furthermore, specified steps can be carried out concurrently unlessexplicit claim language recites that they be carried out separately. Forexample, a claimed step of doing X and a claimed step of doing Y can beconducted simultaneously within a single operation, and the resultingprocess will fall within the literal scope of the claimed process.

EXAMPLES

The examples described herein are intended solely to be illustrative,rather than predictive, and variations in the manufacturing and testingprocedures can yield different results. All quantitative values in theExamples section are understood to be approximate in view of thecommonly known tolerances involved in the procedures used. The foregoingdetailed description and examples have been given for clarity ofunderstanding only. No unnecessary limitations are to be understoodtherefrom.

Materials

Aluminum carbonate (Al₂(CO₃)₃, Alfa Aesar); aluminum chloride (AlCl₃,anhydrous, ≥98.0%, TCl); bis(trifluoromethane)sulfonamide (Tf₂NH,≥95.0%, Sigma-Aldrich); methanesulfonic acid (MsOH, 99%, AcrosOrganics); p-toluenesulphonic acid (TsOH, monohydrate, 98.5+%, AlfaAesar); trifluoromethanesulfonic acid (TfOH, 99%, Oakwood Chemical);trifluoroacetic acid (TFA, 99%, Alfa Aesar); polyvinyl alcohol (PVA,average M_(w) 13000-23000, 98% hydrolyzed, Sigma-Aldrich); ammoniumacetate (CH₃CO₂NH₄, 97%, Alfa Aesar); ammonium hydroxide solution(NH₄OH, ACS reagent, Sigma-Aldrich); and citric acid (97%, Alfa Aesar)were used without further purification.

Example 1 Synthesis of 1 M Al(NTf₂N)₃ Aqueous Solution

To a mixture of Al₂(CO₃)₃ (138 g, 0.59 mol, 1 eq) in H₂O (600 mL), HTf₂Naqueous solution (6 eq., 995 g, 3.54 mol; in 300 mL H₂O) was addedportion-wise under magnetic stirring at room temperature. The turbidmixture foamed and became warm. After 2 h, the mixture was heated at 60°C. overnight and afforded a transparent light yellow liquid. After themixture was cooled down to room temperature, additional H₂O was added tomake the total volume of the mixture 1.2 L.

Example 2 General Procedures for Preparation Aluminum Complex AqueousSolutions for Cyclic Voltammetry (CV) Experiments

To prepare 2 mL aluminum complex aqueous solutions, a mixture ofAl₂(CO₃)₃ (0.23 g, 1 mmol) and H₂O (0.5 mL) was stirred at roomtemperature. Organic acid (6 or 12 mmol; 3 or 6 eq. to Al, see Table 1)was added slowly into the mixture and yielded a turbid aqueous mixture.After stirring for another 1 hour, the mixture was heated toapproximately 60° C. overnight and give a clear liquid. After themixture was cooled to room temperature, H₂O was added to adjust thesolution to certain molarity (0.5 or 1 M, see Table 1).

TABLE 1 Organic acid used (ligand) Reduction Compound in to Al Aluminumonset Compound abbreviation synthesis ratio Molarity/M pH potential/VAluminum chloride AlCl₃ N/A 3:1 1 2.04 −1.67 Aluminum Al(Tf₂N)₃ Tf₂NH3:1 1 1.91 −1.10 bis(trifluoromethane)sulfonimide Al(Tf₂N)₁ 1:1 1 3.30−1.20 Aluminum methanesulfonate Al(MS)₃ MsOH 3:1 1 2.47 −0.84 Al(MS)₆6:1 1 1.00 −1.11 Al(MS)₁ 1:1 3 3.15 −1.12 Aluminum p- Al(OTs)₃ TsOH 3:11 2.36 −1.13 toluenesulphonate Al(OTs)₆ 6:1 0.5 0.24 −0.93 Al(OTs)₆ 6:10.5 1.35 −1.17 Aluminum Al(OTf)₆ TfOH 6:1 1 2.82 −1.35trifluoromethanesulfonate Aluminum trifluoroacetate Al(TFA)₃ TFA 3:1 0.53.17 −1.10 Al(TFA)₆ 6:1 0.5 0.78 only gas evolution Al(TFA)₆ 6:1 0.51.18 −1.07 Al(TFA)₆ 6:1 0.5 3.34 −1.32

TABLE 2 pKa in Ligand Structure water bis(trifluoromethane)sulfonamide(Tf₂N)

Too negative to measure p-Toluenesulfonate (p-TSA)

-2.14 Methanesulfonate (MSO)

-1.61 Triflate (TfO)

-3.43 Trifluoroacetate (TFA)

0.52

Example 3 Hull Cell Experiments Aluminum Plating Experiment 1

An example of the aluminum plating process used 0.3 M Al(Tf₂N)₃ in waterwith an additional electrolyte of 1 M ammonium acetate. An additive of0.5 wt % PVA was added. A hull cell plating was conducted using 100 mLof the solution at 0.5 A for 30 mins giving a powdery deposit at thehigh current density end, no plating at the low current density end anda smooth, reflective, metallic coating between 40 A/dm² and 150 A/dm².The pH of the plating solution was buffered between 4.8 and 5.0, and atemperature of 40° C. The solution is found to contain some dark coloredprecipitate and a large amount of foaming, post electrolysis. A dark,metallic deposit of smooth reflective aluminum is shown by scanningelectron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopyanalysis. See, e.g., FIG. 5.

Aluminum Plating Experiment 2

An additional example of the aluminum plating process used 0.3 MAl(Tf₂N)₃ in water with an additional electrolyte of 1 M ammoniumcitrate which was titrated from 1M citric acid with NH₄OH. An additiveof 0.5 wt % PVA was added. A hull cell plating was conducted using 100mL of the solution at 0.5 A for 30 mins giving a thicker and darkerdeposit at the high current density end (above 40 A/dm²), no plating atthe low current density end (below 40 A/dm2). The coating was thickestat the high current density end and appeared shiny and metallic. The pHof the plating solution was buffered between 2.8 and 3.2, and atemperature of 40° C. The solution is found to contain less dark coloredprecipitate but no foaming was seen in this case, post electrolysis. Athin, dark, metallic deposit of smooth reflective aluminum is shown bySEM and EDX analysis, with a clear deposition gradient from high to lowcurrent density.

Example 4 Small Scale Electroplating of High Purity Aluminum fromAl(OMs)/NH₄ Citrate on a Curved Geometry

Using a 10 mL test aliquot of 0.5 M Al(OMs) and 1 M ammonium citratewith aluminum to ligand ratio of 1:1, a 20 AWG copper wire wassuccessfully plated to a thickness in excess of 10 μm. The procedureused a two electrode system with a copper wire (20 AWG, 6 mm length) asthe cathode substrate and an aluminum counter/reference electrode.Chronopotentiometry was carried out at −20 mA (−120 mA·cm⁻²) for 3 hours(FIG. 5). The temperature of the bath was controlled and maintained at54° C. throughout.

Example 5

A range of aluminum salts with various ligand structures have beendeveloped (see Table 2). The ligands are generally considered asmono-dentate, with the exception of Tf₂N which is more likely abidentate ligand. Each ligand is considered as electron withdrawing innature to varying degrees. While not being bound by any specific theory,it is believed that this electron withdrawing character is likely toshift the reduction potential of aluminum (or any other metal describedherein) with the most strongly electron withdrawing substituents leadingto a shift towards less negative potentials. FIG. 2 shows thecomparative electron withdrawing character of each substituent asestimated from the pKa of the acid. Generally speaking, stronger acidsare more able to stabilize the deprotonated form of the acid leading tolower pKas.

In order to test the effect of various electron withdrawing substituentson the standard reduction potential of aluminum complexes a series ofcyclic voltammetry experiments were carried out. Each salt wassynthesized in situ by combination of various acids with aluminumcarbonate in water to make a 1 M solution of each salt. In order tolimit ligand substitution and complexation, no other electrolyte wasadded into the solution. Each cyclic voltammogram was collected vs.Ag/AgCl (3 M NaCl) and used an aluminum counter electrode. The workingelectrode was chosen as glassy carbon to limit the hydrogen evolutionreaction which would ordinarily obscure the aluminum reduction for somesalts.

As a control case 1 M AlCl₃ was used to gauge the effectiveness of theelectron withdrawing substituents. It was expected that for aluminumchloride it is likely that the electroactive species is of an aqueousaluminum hydroxide complex (Al[H₂O]₅OH), which forms rapidly upon AlCl₃exposure to excess water. This aluminum complex was initially comparedto Al(Tf₂N)₃ (FIG. 2) and it was found that the electron withdrawingTf₂N ligands had a significant effect on the cathodic reduction process.The onset potential was shifted from about −1.65 V to about −1.1 V.While not being bound by any particular theory, it is believed that thisshift in reduction potential shows that the aluminum species may be in adifferent form from the AlCl₃ case and does not simply become a waterhydroxide complex. This might suggest that the ligand structure might besubstantially retained in water and remains stable in solution formonths. This development in aqueous aluminum complexation andcomparative ease of electroreduction allows for greater competition ofaluminum reduction with hydronium reduction on metal substrates, thusopening an aqueous aluminum plating procedure. Further evidence thataluminum electroplating is possible in this system comes from thepresence of a nucleation loop in a reverse scan. This suggests anucleation event occurs on the cathodic wave, likely the surfaceadsorption of a reduced aluminum species.

Additional salts (see Table 2) have been tested in a similar procedurewith some salts showing similar promise for aluminum reduction. Otherligands were tested in a 1:1, 1:3 and 1:6 ratio of aluminum to ligand totest the effect of a 6 coordinate complex vs. a 1 or 3 coordinatecomplex. In the case of a hexa-coordinate aluminum species, anadditional effect was that excess acid caused the pH to be reducedsignificantly.

When p-TSA is used as the ligand in both a 1:4 and 1:6 ratio with Al³⁺ asystematic shift is seen towards more positive reduction potentials. Asthe solution becomes more acidic, it would be expected that hydroniumreduction would become more prevalent at more positive potentials. Inthe case of 6 M unbound p-TSA (FIG. 3 scan (i)) a solvent reduction waveis visualized with a low onset and no mass transport limiting peak. Whenthe same amount of p-TSA is used in a 1:6 molar ratio with aluminum asimilar onset is seen (FIG. 3 scan (ii)) but now a peak emerges which,when compared with Al(Tf₂N)₃ may be attributed to an Al³⁺ reductionevent from a p-TSA rich complex. In a 1:4 ratio with aluminum (FIG. 3scan (iii)), a more negative onset and peak is seen as well as largerresistance. This discrepancy may be explained in part by pH shift sinceit would be expected that the excess acid would lead to a dramaticreduction in solution pH. Indeed, the pH of the 1:6 solution is about0.24 and may explain the early onset of hydronium reduction. When the pHof this solution was adjusted by addition of ammonium hydroxide to pH1.35 the redox behavior is identical to that of the 1:4 solution (FIG.3, scans (iii) and (iv)). This behavior shows that the redox process isthe same in both cases and that the aluminum coordination is likely by1-4 p-TSA, is stable in acidic media and has a lower reduction potentialthan Al(H₂O)OH²⁺.

Methanesulfonate (MS) is a comparable ligand to p-TSA, showing highlyelectron withdrawing character but is sterically much smaller, which maybe expected to facilitate a hexa-coordinate aluminum species. It isfound that both the 1:1 and 6:1 ligand to aluminum ratio cases have verysimilar onsets for aluminum reduction of ca. −1.1V. However the 3:1 caseshows an onset of only −0.84 V. This suggests that a maximized effectfor electron withdrawing ligands is found for this ratio with lowercoordination (1:1) being very similar in onset to other tested ligandsand 6:1 having an excess of acid and ligands. The 3:1 case also has a pHof only 2.47 suggesting that a lot of the expected free protons are lostupon reaction with the carbonate and the ligands are likely coordinatedrather than the aluminum complex leading to a high hydronium ionconcentration.

Triflate (TfO) showed very little evidence of ligation to aluminum witha 6:1 ratio of acid showing a highly acidic environment with a pH of 0.This suggests that the majority of the acid remains free and is notinvolved in the anticipated carbonate displacement reaction and leads toalmost no aluminum ligation. This hypothesis is corroborated by therelatively negative reduction potential compared to other ligands of−1.35 V.

The final ligand Trifluoroacetate (TFA) was different from the others byway of a coordinating acetate anion rather than a sulfonate. For thecase of a 1:3 complex for aluminum to TFA, a similar character was seento that of both p-TSA and TfO with an onset potential of ca −1.10 V anda resistive peak being found, suggesting very few charge carriers beingavailable. With a 1:6 ratio of aluminum to TFA a much lower onsetpotential was found although it is highly likely that the majority ofthis process was proton reduction with no clear aluminum onset beingdetectable. When the pH was adjusted for the 1:6 solution to make itmost similar to that of the 1:3 a much higher onset potential was found.This suggests a different reductive aluminum species as compared to the1:3 case, although the reduction was also not similar in character tothat of Al(H₂O)₅OH and thus it must be determined that TFA is able to atleast partially coordinate to the aluminum center and affect itselectronegativity.

In summary, Al(MS)₃ shows the lowest recorded potential for Al³⁺reduction below that for hydronium reduction with an onset of about−0.84 V and a peak at about −1.3 V. See, e.g., FIG. 4. Hydrogengeneration is obvious at the higher limit of this voltage range but anappreciable current for aluminum reduction is established prior to theevolution of gas. Other ligands p-TSA and Tf₂N show a comparable loweredreduction potential although slightly more negative than MS. It isunclear what the coordination for the p-TSA ligand is to aluminum, andis likely to be able to coordinate at least three p-TSA ligands. Thiscoordination is sufficient to substantially lower the reductionpotential of Al³⁺ and is visible proceeding hydronium reduction at pHsas low as 1.35. TfO however, seems to be unstable in the presence of NH₄⁺ and is likely not strongly coordinating, with a redox process mostsimilar to that of the water hydrated aluminum species. TFA appears tobe an intermediate case whereby a lower coordination number may bepossible in conjunction with some hydration. A slightly improvedreduction potential is recorded, although not sufficient to compete witheither Tf₂N or p-TSA.

It will be apparent to those skilled in the art that the specificstructures, features, details, configurations, etc., that are disclosedherein are simply examples that can be modified and/or combined innumerous embodiments. All such variations and combinations arecontemplated by the inventor as being within the bounds of thisdisclosure. Thus, the scope of the disclosure should not be limited tothe specific illustrative structures described herein, but ratherextends at least to the structures described by the language of theclaims, and the equivalents of those structures. To the extent thatthere is a conflict or discrepancy between this specification as writtenand the disclosure in any document incorporated by reference herein,this specification as written will control.

The present invention provides for the following exemplary embodiments,the numbering of which is not to be construed as designating levels ofimportance:

Embodiment 1 relates to a method for the electrodeposition of at leastone metal onto a surface of a conductive substrate at a temperature fromabout 10° C. to about 70° C., about 0.5 atm to about 5 atm, in anatmosphere comprising oxygen, the method comprising electrodepositingthe at least one metal via electrochemical reduction of a metal complexdissolved in a substantially aqueous medium.

Embodiment 2 relates to the method of Embodiment 1, wherein the metalcomprises at least one of reactive and non-reactive metals.

Embodiment 3 relates to the method of Embodiment 2, wherein the reactivemetal comprises at least one of aluminum, titanium, manganese, gallium,vanadium, zinc, zirconium, and niobium.

Embodiment 4 relates to the method of Embodiment 2, wherein thenon-reactive metal comprises at least one of tin, gold, copper, silver,rhodium, and platinum.

Embodiment 5 relates to the method of Embodiments 1-4, wherein the metalcomplex comprises a metal center and ligands, wherein at least one ofthe ligands is an electron withdrawing ligand

Embodiment 6 relates to the method of Embodiment 5, wherein the ligandsare sufficiently electron withdrawing such that the reduction potentialof the metal in the metal complex is decreased below the over-potentialfor the evolution of hydrogen gas due to water splitting.

Embodiment 7 relates to the method of Embodiments 5-6, wherein theligands are at least one of sulfonate ligands and sulfonimide ligands.

Embodiment 8 relates to the method of Embodiment 7, wherein the at leastone sulfonate ligands is a ligand of the formula SO₃R¹, wherein R¹ ishalo; substituted or unsubstituted C₆-C₁₈-aryl; substituted orunsubstituted C₁-C₆-alkyl; substituted or unsubstitutedC₆-C₁₈-aryl-C₁-C₆-alkyl.

Embodiment 9 relates to the method of Embodiment 7, wherein the at leastone sulfonimide ligand is a ligand of the formula N(SO₃R¹), wherein R¹is wherein R¹ is halo; substituted or unsubstituted C₆-C₁₈-aryl;substituted or unsubstituted C₁-C₆-alkyl; substituted or unsubstitutedC₆-C₁₈-aryl-C₁-C₆-alkyl.

Embodiment 10 relates to the method of Embodiment 7-9, wherein the atleast one sulfonate ligand comprises a sulfonate ligand of the formulae:

Embodiment 11 relates to the method of Embodiment 7, wherein the atleast one sulfonimide ligand comprises a sulfonimide ligand of theformula:

Embodiment 12 relates to the method of Embodiments 1-11, wherein themetal complex is at least one metal complex of the formulaAl(SO₃R¹)_(n), wherein R¹ is halo; substituted or unsubstitutedC₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl; substituted orunsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl; n is an integer from 2 to 8; andAl[N(SO₃R¹)₂]_(n), wherein R¹ is halo; substituted or unsubstitutedC₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl; substituted orunsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl; and n is an integer from 1 to 4.

Embodiment 13 relates to the method of Embodiments 1-12, wherein thesubstantially aqueous medium comprises an electrolyte.

Embodiment 14 relates to the method of Embodiment 13, wherein theelectrolyte comprises at least one of a halide electrolyte; aperchlorate electrolyte; an amidosulfonate electrolyte;hexafluorosilicate electrolyte; a tetrafluoroborate electrolyte;methanesulfonate electrolyte; and a carboxylate electrolyte.

Embodiment 15 relates to the method of Embodiments 13-14, wherein theelectrolyte comprises at least one of compounds of the formula R³CO₂ ⁻,wherein R³ is substituted or unsubstituted C₆-C₁₈-aryl; or substitutedor unsubstituted C₁-C₆-alkyl;

Embodiment 16 relates to the method of Embodiments 13-15, wherein theelectrolyte comprises at least one of polycarboxylates; and lactones.

Embodiment 17 relates to the method of Embodiments 1-16, wherein the pHof the substantially aqueous medium is buffered at a pH of about 1 andabout 7.

Embodiment 18 relates to the method of Embodiments 1-17, wherein thesubstantially aqueous medium comprises a water-miscible organic solvent.

Embodiment 19 relates to the method of Embodiment 18, wherein thewater-miscible organic solvent comprises at least one of anC₁-C₆-alkanol, a C₂-C₁₀-polyol, a (poly)alkylene glycol ether, aC₂-C₁₀-carboxylic acid; a C₂-C₁₀-ketone; a C₂-C₁₀-aldehyde; apyrrolidone; a C₂-C₁₀-nitrile; a phthalate; a C₂-C₁₀-dialkylamine; aC₂-C₁₀-dialkylformamide; a C₂-C₁₀-dialkyl sulfoxide; aC₄-C₁₀-heterocycloalkane; an aminoalcohol; and a C₄-C₁₀-heteroarylene.

Embodiment 20 relates to the method of Embodiment 19, wherein theC₁-C₆-alkanol comprises ethanol.

Embodiment 21 relates to the method of Embodiments 1-, wherein theelectrodepositing comprises electrodepositing at least one layer of theat least one metal onto a surface of the substrate.

Embodiment 22 relates to the method of Embodiments 1-21, wherein theelectrodepositing comprises electrodepositing at least two layers of theat least one metal onto a surface of the substrate.

Embodiment 23 relates to the method of Embodiment 22, wherein the firstlayer comprises different at least one metal relative to the secondlayer.

1.-23. (canceled)
 24. A method for electrodeposition of at least onereactive metal onto a surface of a conductive substrate at a temperaturefrom about 10° C. to about 70° C., about 0.5 atm (50.66 kPa) to about 5atm (506.62 kPa), in an atmosphere comprising oxygen, the methodcomprising electrodepositing the at least one reactive metal viaelectrochemical reduction of a metal complex dissolved in asubstantially aqueous medium the metal complex comprising a metal centerand ligands; wherein: the reactive metal comprises at least one ofaluminum, titanium, manganese, gallium, vanadium, zirconium, andniobium; and the ligands are at least one of sulfonate ligands andsulfonimide ligands.
 25. The method of claim 24, wherein the at leastone sulfonate ligand is a ligand of a formula SO₃R¹, wherein R¹ is halo;substituted or unsubstituted C₆-C₁₈-aryl; substituted or unsubstitutedC₁-C₆-alkyl; and substituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl.26. The method of claim 24, wherein the at least one sulfonimide ligandis a ligand of a formula N(SO₂R¹), wherein R¹ is halo; substituted orunsubstituted C₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl; andsubstituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl.
 27. The method ofclaim 24, wherein the at least one sulfonate ligand comprises asulfonate ligand of a formulae:


28. The method of claim 24, wherein the at least one sulfonimide ligandcomprises a sulfonimide ligand of a formula:


29. The method of claim 24, wherein the metal complex is at least onemetal complex of a formula Al(SO₃R¹)_(n), wherein R¹ is halo;substituted or unsubstituted C₆-C₁₈-aryl; substituted or unsubstitutedC₁-C₆-alkyl; n is an integer from 2 to 8; and Al[N(SO₃R¹)₂]_(n), whereinR¹ is halo; substituted or unsubstituted C₆-C₁₈-aryl; substituted orunsubstituted C₁-C₆-alkyl; substituted or unsubstitutedC₆-C₁₈-aryl-C₁-C₆-alkyl; and n is an integer from 1 to
 4. 30. The methodof claim 24, wherein the substantially aqueous medium comprises anelectrolyte.
 31. The method of claim 30, wherein the electrolytecomprises at least one of a halide electrolyte; a perchlorateelectrolyte; an amidosulfonate electrolyte; hexafluorosilicateelectrolyte; a tetrafluoroborate electrolyte; methanesulfonateelectrolyte; and a carboxylate electrolyte.
 32. The method of claim 31,wherein the electrolyte comprises at least one of compounds of a formulaR³CO₂—, wherein R³ is substituted or unsubstituted C₆-C₁₈-aryl; orsubstituted or unsubstituted C₁-C₆-alkyl.
 33. The method of claim 31,wherein the electrolyte comprises at least one of polycarboxylates; andlactones.
 34. The method of claim 24, wherein the pH of thesubstantially aqueous medium is buffered at a pH from about 1 to about7.
 35. The method of claim 24, wherein the substantially aqueous mediumcomprises a water-miscible organic solvent.
 36. The method of claim 35,wherein the water-miscible organic solvent comprises at least one of anC₁-C₆-alkanol, a C₂-C₁₀-polyol, a (poly)alkylene glycol ether, aC₂-C₁₀-carboxylic acid; a C₂-C₁₀-ketone; a C₂-C₁₀-aldehyde; apyrrolidone; a C₂-C₁₀-nitrile; a phthalate; a C₂-C₁₀-dialkylamine; aC₂-C₁₀-dialkylformamide; a C₂-C₁₀-dialkyl sulfoxide; aC₄-C₁₀-heterocycloalkane; an aminoalcohol; and a C4-C10-heteroarylene.37. The method of claim 36, wherein the C₁-C₆-alkanol comprises ethanol.38. The method of claim 24, wherein the electrodepositing compriseselectrodepositing at least one layer of the at least one metal onto thesurface of the substrate.
 39. The method of claim 24, wherein theelectrodepositing comprises electrodepositing at least a first layer anda second layer of the at least one metal onto the surface of thesubstrate.
 40. The method of claim 39, wherein the first layer comprisesa different at least one metal relative to the second layer.
 41. Amethod for electrodeposition of at least one metal onto a surface of aconductive substrate at a temperature from about 10° C. to about 70° C.,about 0.5 atm (50.66 kPa) to about 5 atm (506.62 kPa), in an atmospherecomprising oxygen, the method comprising electrodepositing the at leastone metal via electrochemical reduction of a metal complex dissolved ina substantially aqueous medium; wherein: the metal complex comprises ametal center and ligands, wherein at least one of the ligands is anelectron withdrawing ligand and the ligands are sufficiently electronwithdrawing such that the reduction potential of the metal in the metalcomplex is decreased below the over-potential for the evolution ofhydrogen gas due to water splitting; and the at least one metal is atleast one of reactive and non-reactive metals; or the ligands are atleast one of sulfonate ligands and sulfonimide ligands.
 42. A method forelectrodeposition of at least one reactive metal onto a surface of aconductive substrate at a temperature from about 10° C. to about 70° C.,about 0.5 atm (50.66 kPa) to about 5 atm (506.62 kPa), in an atmospherecomprising oxygen, the method comprising electrodepositing the at leastone reactive metal via electrochemical reduction of a metal complexdissolved in a substantially aqueous medium; wherein: the reactive metalcomprises at least one of aluminum, titanium, manganese, gallium,vanadium, zirconium, and niobium; and the metal complex comprises ametal center and ligands, wherein at least one of the ligands is anelectron withdrawing ligand, and are sufficiently electron withdrawingsuch that the reduction potential of the metal in the metal complex isdecreased below the over-potential for the evolution of hydrogen gas dueto water splitting.
 43. A method for electrodeposition of at least onereactive metal onto a surface of a conductive substrate at a temperaturefrom about 10° C. to about 70° C., about 0.5 atm (50.66 kPa) to about 5atm (506.62 kPa), in an atmosphere comprising oxygen, the methodcomprising electrodepositing the at least one reactive metal viaelectrochemical reduction of a metal complex dissolved in a medium thatis at least about 50% aqueous, the metal complex comprising a metalcenter and ligands; wherein: the reactive metal comprises at least oneof aluminum, titanium, manganese, gallium, vanadium, zirconium, andniobium; and the ligands are at least one of sulfonate ligands andsulfonimide ligands.
 44. The method of claim 43, wherein the medium isat least about 60% aqueous.
 45. The method of claim 44, wherein themedium is at least about 70% aqueous.
 46. The method of claim 45,wherein the medium is at least about 80% aqueous.
 47. The method ofclaim 46, wherein the medium is at least about 90% aqueous.
 48. Themethod of claim 47, wherein the medium is at least about 99% aqueous.49. The method of claim 24, wherein the reactive metal is aluminum, andthe medium consists essentially of water.